"Overconfidence leads to bad play."

As an avid chess player, I can tell you that this is true in chess as well. People look at brilliant sacrifices by grandmasters (Bobby Fischer was famous for this) and think they are brilliant enough to pull off the same thing. In my experience, 80-90% of material sacrifices fail. When they do succeed, it is usually because the sacrificer is considerably better than her opponent. I've learned to subdue my desire for a sacrifice and a quick strike and work on a longterm plan instead.